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<table width="100%" summary="page for lettuce"><tr><td>lettuce</td><td style="text-align: right;">R Documentation</td></tr></table>

<h2>Hormesis in lettuce plants</h2>

<h3>Description</h3>

<p>Data are from an experiment where isobutylalcohol was dissolved in a nutrient solution in which lettuce
(<em>Lactuca sativa</em>) plants were grown. The plant biomass of the shoot was determined af 21 days.
</p>


<h3>Usage</h3>

<pre>data(lettuce)</pre>


<h3>Format</h3>

<p>A data frame with 14 observations on the following 2 variables.
</p>

<dl>
<dt>conc</dt><dd><p>a numeric vector of concentrations of isobutylalcohol (mg/l)</p>
</dd>
<dt>weight</dt><dd><p>a numeric vector of biomass of shoot (g)</p>
</dd>
</dl>



<h3>Details</h3>

<p>The data set illustrates hormesis, presence of a subtoxic stimulus at low concentrations.
</p>


<h3>Source</h3>

<p>van Ewijk, P. H. and Hoekstra, J. A. (1993) 
Calculation of the EC50 and its Confidence Interval When Subtoxic Stimulus Is Present,
<em>ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY</em>, <b>25</b>, 25&ndash;32.
</p>


<h3>References</h3>

<p>van Ewijk, P. H. and Hoekstra, J. A. (1994) 
Curvature Measures and Confidence Intervals for the Linear Logistic Model,
<em>Appl. Statist.</em>, <b>43</b>, 477&ndash;487.
</p>


<h3>Examples</h3>

<pre>

## Look at data
lettuce

## Monotonous dose-response model
lettuce.m1 &lt;- drm(weight~conc, data=lettuce, fct=LL.3())

plot(lettuce.m1, broken = TRUE)

## Model fit in van Ewijk and Hoekstra (1994)
lettuce.m2 &lt;- drm(weight~conc, data=lettuce, fct=BC.4())
modelFit(lettuce.m2)

plot(lettuce.m2, add = TRUE, broken = TRUE, type = "none", lty = 2)

## Hormesis effect only slightly significant
summary(lettuce.m2)

## Hormesis effect highly significant
##  compare with t-test for the "f" parameter in the summary output)
anova(lettuce.m1, lettuce.m2)

</pre>


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